1. Field of the Invention
The present invention generally relates to a spine formation device to form a spine of a bundle of folded sheets, a post-processing apparatus including the spine formation device, and a bookbinding system including the spine formation device and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine capable of at least two of these functions.
2. Discussion of the Background Art
Post-processing apparatuses to perform post processing of recording media, such as aligning, sorting, stapling, punching, and folding of sheets, are widely used and are often disposed downstream from an image forming apparatus to perform post-processing of the sheets output from the image forming apparatus. At present, post-processing apparatuses generally perform saddle-stitching along a centerline of sheets in addition to conventional edge-stitching along an edge portion of sheets.
However, when a bundle of sheets (hereinafter “booklet”) is saddle-stitched or saddle-stapled and then folded in two, its folded portion, that is, a portion around its spine, tends to bulge, degrading the overall appearance of the booklet. In addition, the bulging spine makes the booklet thicker on the spine side and thinner on the opposite side, making it difficult to stack, store, or transport them. Flattening the spines of the booklets improves their appearance and allows a relatively large number of booklets to be piled together with ease.
It is to be noted that the term “spine” used herein means not only the stitched side of the booklet but also portions of the front cover and the back cover continuous with the spine.
To improve the quality of the finished product, several approaches, described below, for shaping the folded portion of a bundle of saddle-stitched sheets have been proposed.
For example, in JP-2001-260564-A, the spine of the booklet is flattened using a pressing member configured to sandwich an end portion of the booklet adjacent to the spine and a spine-forming roller serving as a spine pressing member configured to roll in a longitudinal direction of the spine while contacting the spine of the booklet. The spine-forming roller moves at least once over the entire length of the spine of the booklet being fixed by the pressing member while applying to the spine a pressure sufficient to flatten the spine.
Although this approach can flatten the spine of the booklet to a certain extent, it is possible that the sheets might wrinkle and be torn around the spine or folded portion because the pressure roller applies localized pressure to the spine continuously. Further, it takes longer to flatten the spine because the pressure roller must move over the entire length of the spine of the booklet.
Moreover, this approach does not consider stapled booklets. More specifically, when staples project from the surface of the spine of the booklet, the spine pressing member simply presses the staples upstream in the direction in which the booklet is transported, thus making the surface of the spine uneven and degrading the appearance of the booklet.
To address the above-described problem, for example, JP-2007-237562-A proposes a spine formation device that includes a sandwiching member that sandwiches the booklet from the front side and the back side of the booklet, a pressure member disposed downstream from the sandwiching member in a direction in which the bundle of folded sheets is transported, and a spine pressing member (i.e., a spine pressing plate) that is pressed against the spine of the booklet. After the spine pressing plate is pressed against the spine of the booklet, the pressure member squeezes the spine from the side, that is, in the direction of the thickness of the booklet to reduce bulging of the spine.
This configuration can reduce the pressure exerted on the spine and accordingly reduce damage to the spine compared with the first method described above, in which the spine formation member applies relatively high pressure to the spine while moving along the spine.
Additionally, in the second method, recessed portions are formed in the surface of the spine pressing plate pressing against the spine to accommodate objects such as loop stitches projecting from the spine of the booklet.
However, although aiming at eliminating adverse effects caused by the objects projecting from the spine in spine formation, the second method is not very flexible in application. For example, this configuration cannot accommodate changes in the size of interval between staples or changes in the number of staples used in the booklet.
In view of the foregoing, the inventors of the present invention recognize that there is a need for an apparatus capable of flattening the spine of the booklet regardless of the position or the number of staples in used in the booklet.